Fix String#toLower/UpperCase usages

Author: electronicboy

paper-api/src/main/java/com/destroystokyo/paper/NamespacedTag.java

@@ -75,7 +75,7 @@ public NamespacedTag(@NotNull Plugin plugin, @NotNull String key) {
         Preconditions.checkArgument(key != null, "Key cannot be null");
 
         this.namespace = plugin.getName().toLowerCase(Locale.ROOT);
-        this.key = key.toLowerCase().toLowerCase(Locale.ROOT);
+        this.key = key.toLowerCase(Locale.ROOT);
 
         // Check validity after normalization
         Preconditions.checkArgument(VALID_NAMESPACE.matcher(this.namespace).matches(), "Invalid namespace. Must be [a-z0-9._-]: %s", this.namespace);

paper-server/src/main/java/io/papermc/paper/configuration/PaperConfigurations.java

@@ -51,6 +51,7 @@
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 import java.util.List;
+import java.util.Locale;
 import java.util.function.Function;
 import java.util.function.Supplier;
 
@@ -150,7 +151,7 @@ public class PaperConfigurations extends Configurations<GlobalConfiguration, Wor
         """;
 
     @VisibleForTesting
-    public static final Supplier<SpigotWorldConfig> SPIGOT_WORLD_DEFAULTS = Suppliers.memoize(() -> new SpigotWorldConfig(RandomStringUtils.randomAlphabetic(255), Key.key(RandomStringUtils.randomAlphabetic(255).toLowerCase())) {
+    public static final Supplier<SpigotWorldConfig> SPIGOT_WORLD_DEFAULTS = Suppliers.memoize(() -> new SpigotWorldConfig(RandomStringUtils.randomAlphabetic(255), Key.key(RandomStringUtils.randomAlphabetic(255).toLowerCase(Locale.ROOT))) {
         @Override // override to ensure "verbose" is false
         public void init() {
             SpigotConfig.readConfig(SpigotWorldConfig.class, this);

test-plugin/src/main/java/io/papermc/testplugin/brigtests/example/IceCreamTypeArgument.java

@@ -12,14 +12,15 @@
 import net.kyori.adventure.text.format.NamedTextColor;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.Locale;
 import java.util.concurrent.CompletableFuture;
 
 public class IceCreamTypeArgument implements CustomArgumentType.Converted<IceCreamType, String> {
 
     @Override
     public @NotNull IceCreamType convert(String nativeType) throws CommandSyntaxException {
         try {
-            return IceCreamType.valueOf(nativeType.toUpperCase());
+            return IceCreamType.valueOf(nativeType.toUpperCase(Locale.ROOT));
         } catch (IllegalArgumentException ignored) {
             throw new ComponentCommandExceptionType(Component.text("Invalid species %s!".formatted(nativeType), NamedTextColor.RED)).create();
         }